The present invention is directed to cementitious mixtures containing pozzolanic cement replacement materials. More particularly, the present invention is directed to cementitious mixtures containing high percentages of pozzolan cement replacement, and compatabilizing admixtures therefor.
Over the years, the use of cementitious materials as a partial replacement for portland cement in concrete has become an increasingly attractive alternative to portland cement alone. The desire to increase the use of fly ash, blast furnace slag, and natural pozzolanic cement in concrete mixtures can be attributed to several factors. These include cement shortages, economic advantages of portland cement replacement, improvements in permeability of the concrete product, and lower heats of hydration.
The growth in the use of higher amounts of pozzolanic cement replacements, such as fly ash for example, in concrete has been impaired by the potential incompatibility exhibited by these materials, especially when used at high percentages, in combination with water reducing admixtures. Water reducers are desirable to decrease the amount of water required in the preparation of the cementitious mixtures, and to increase the strength of the resulting concrete. However, the incompatibility of the pozzolan replacement materials with water reducing admixtures can result in the significant retardation of the initial and final setting of the concrete containing both these materials.
Despite the cost and performance advantages of fly ash, slag, calcined clay, and natural pozzolans as partial replacements of portland cement in concrete, there are practical limitations to the amount at which they can be used in the cementitious mixture. Using these materials at higher levels, such as above about 10 to 15 weight percent based on the weight of the portland cement, can result in the retarded setting time of the concrete up to several hours, and perhaps longer depending upon the ambient temperature. This incompatibility puts a burden of increased costs and time on the end user which is unacceptable.
While it is known to use set time accelerators in concrete mixtures, these accelerator admixtures have been ineffective in solving the compatibility problem that exists in high pozzolan replacement/portland cement mixtures, particularly when used with water reducing admixtures, so that set time is not able to be decreased to an acceptable level. The use of accelerators with water reducers, such as naphthalene sulfonates, lignin and substituted lignins, melamine and the like, has been ineffective to produce an acceptable high pozzolanic replacement containing hydraulic cement based cementitious mixture with normal setting characteristics and an acceptable resulting concrete.
U.S. Pat. Nos. 4,373,956 and 4,473,405 disclose various admixture compositions for incorporation into hydraulic cement mixes to accelerate the rate of hardening and setting. U.S. Pat. No. 4,337,094 discloses combinations of additives which can be used to accelerate the setting time of portland type cements. These additives, when used in cementitious mixtures containing portland cement and high proportions of pozzolan cement replacements, as well as a water reducer, cannot compensate for the retardation of setting time induced in the mixtures by the cement replacement and water reducer, and thus do not acceptably accelerate the mixture to setting.
U.S. Pat. No. 5,556,458 discloses a cementitious composition containing a high percentage of fly ash and hydraulic cement, but in which a fly ash containing a particular calcium oxide content is required and a water reducing admixture is not present. The composition is useful for quick setting repair mortar type products.
What is required by the industry, however, is a cementitious mixture capable of forming concrete which contains a significant percentage of cement replacement material (to replace a portion of the hydraulic cement, such as portland cement) for performance and cost considerations, and water reducers to decrease water usage and increase compressive strength, the components in such cementitious mixtures being compatible and which mixtures set in an industry-acceptable time period.
U.S. Pat. No. 5,158,996 and patent publication EP753488, both of which are hereby incorporated by reference herein, disclose polymer additives useful as additives, such as dispersants, for cement mixtures, but their use with high pozzolan replacement/portland cement mixtures has not previously been considered.
It is therefore an object of the invention to provide a cementitious mixture which contains a significant proportion of pozzolan cement replacement materials for hydraulic cement, such as portland cement, as well as water reducing materials, which have acceptable or improved compressive strength.
It is another object of the invention to provide a cementitious mixture which contains a significant proportion of pozzolan cement replacement materials for hydraulic cement, such as portland cement, as well as water reducing materials, which set in an industry-acceptable time period.
It is another object of the invention to provide a method for preparing a cementitious material which contains a significant proportion of pozzolan cement replacement materials for hydraulic cement, such as portland cement, as well as water reducing materials, which have acceptable or improved compressive strength and which set in an industry-acceptable time period.
It is another object of the invention to provide a compatabilizing admixture for cementitious mixtures which contain a significant proportion of pozzolan cement replacement materials for hydraulic cement, such as portland cement, which admixtures provide water reducing means for imparting acceptable or improved compressive strength, and set accelerating means for inducing the mixture to set in an industry-acceptable time period.
The present invention is directed to a compatabilizing admixture for cementitious mixtures containing hydraulic cement and greater than about 10 percent pozzolanic cement replacement by weight of the portland cement and cement replacement, comprising a derivatized polycarboxylate dispersant which is a polymer comprising units derived from at least one of a substituted carboxylic acid monomer and a substituted ethylenically unsaturated monomer, at least one of an N-polyoxyalkylene maleimide and a condensation product of an unsubstituted carboxylic acid monomer and an alkoxypolyoxyalkylene primary amine substituted carboxylic acid monomer, and optionally including an unsaturated hydrocarbon, in combination with a set accelerator for concrete. The derivatized polycarboxylate dispersant preferably has the general structure shown below: 
where:
D=a component selected from the group consisting of the structure d1, the structure d2, and mixtures thereof;
X=H, CH3, C2 to C6 Alkyl, Phenyl, Substituted Phenyl such as p-Methyl Phenyl, Sulfonated Phenyl;
Y=H, xe2x80x94COOM;
R=H, CH3;
Z=H, xe2x80x94SO3M, xe2x80x94PO3M, xe2x80x94COOM, xe2x80x94OR3, xe2x80x94COOR3, xe2x80x94CH2OR3, xe2x80x94CONHR3, xe2x80x94CONHC(CH3)2 CH2SO3M, xe2x80x94COO(CHR4)nOH where n=about 2 to about 6;
R1, R2, R3, R5 are each independently xe2x80x94(CH2CHRO)mR4 random copolymer of oxyethylene units and oxypropylene units where m=about 10 to about 500 and wherein the amount of oxyethylene in the random copolymer is from about 60% to 100% and the amount of oxypropylene in the random copolymer is from 0% to about 40%;
R4=H, Methyl, C2 to about C6 Alkyl, about C6 to about C10 aryl;
M=H, Alkali Metal, Alkaline Earth Metal, Amnmonia, Amine, Substituted Amine such as triethanol amine, Methyl, C2 to about C6 Alkyl;
a=0 to about 0.8, preferably 0 to about 0.6, and most preferably 0 to about 0.5;
b=About 0.2 to about 0.99, preferably about 0.3 to about 0.99, and most preferably about 0.4 to about 0.99;
c=0 to about 0.5, preferably 0 to about 0.3, and most preferably 0 to about 0.1;
d=0 to about 0.5, preferably 0 to about 0.3, and most preferably 0 to about 0.1;
xe2x80x83and
xe2x80x83wherein a, b, c, and d represent the mole fraction of each unit and the sum of a, b, c, and d is 1.0, and wherein at least one of c and d is greater than 0.
The pozzolan cement replacement for a portion of the portland cement, according to the present invention, includes at least one of fly ash (such as Class C fly ash and Class F fly ash), blast furnace slag, calcined clay, and natural pozzolanic materials. xe2x80x9cNatural pozzolansxe2x80x9d is a term of art used in the cementitious formulation industry and is well known to those of ordinary skill in the art to mean those pozzolans that are naturally occurring as opposed to blast furnace slag or fly ash, which are produced by man-made processes. Naturally occurring pozzolans include volcanic tuffs and pumices, trasses, diatomaceous earths, opaline cherts, and some shales. Preferably, up to 50 percent of the portland cement in the cementitious product is replaced by the pozzolanic cement replacement material.
The present invention further provides a method for preparing a cementitious material comprising mixing a hydraulic cement with a pozzolanic cement replacement selected from fly ash, slag, natural pozzolans, and mixtures thereof, and a compatabilizing admixture, wherein the compatabilizing admixture comprises the above described derivatized polycarboxylate water reducing dispersant, in combination with an accelerator for concrete. In one embodiment, the method uses a compatabilizing admixture which comprises a derivatized polycarboxylate dispersant comprising a polymer of the general structure shown below: 
where:
D=a component selected from the group consisting of the structure d1, the structure d2, and mixtures thereof;
X=H, CH3, C2 to C6 Alkyl, Phenyl, Substituted Phenyl such as p-Methyl Phenyl, Sulfonated Phenyl;
Y=H, xe2x80x94COOM;
R=H, CH3;
Z=H, xe2x80x94SO3M, xe2x80x94PO3M, xe2x80x94COOM, xe2x80x94OR3, xe2x80x94COOR3, xe2x80x94CH2OR3, xe2x80x94CONHR3, xe2x80x94CONHC(CH3)2 CH2SO3M, xe2x80x94COO(CHR4)nOH where n=about 2 to about 6;
R1, R2, R3, R5 are each independently xe2x80x94(CH2CHRO)mR4 random copolymer of oxyethylene units and oxypropylene units where m=about 10 to about 500 and wherein the amount of oxyethylene in the random copolymer is from about 60% to 100% and the amount of oxypropylene in the random copolymer is from 0% to about 40%;
R4=H, Methyl, C2 to about C6 Alkyl, about C6 to about C10 aryl;
M=H, Alkali Metal, Alkaline Earth Metal, Ammonia, Amine, Substituted Amine such as triethanol amine, Methyl, C2 to about C6 Alkyl;
a=0 to about 0.8, preferably 0 to about 0.6, and most preferably 0 to about 0.5;
b=About 0.2 to about 0.99, preferably about 0.3 to about 0.99, and most preferably about 0.4 to about 0.99;
c=0 to about 0.5, preferably 0 to about 0.3, and most preferably 0 to about 0.1;
d=0 to about 0.5, preferably 0 to about 0.3, and most preferably 0 to about 0.1;
xe2x80x83and
xe2x80x83wherein a, b, c, and d represent the mole fraction of each unit and the sum of a, b, c, and d is 1.0, and wherein at least one of c and d is greater than 0.
The present invention further comprises a compatabilizing admixture for cementitious mixtures containing hydraulic cement and greater than about 10 percent pozzolanic cement replacement based on total weight of the cement and cement replacement, comprising the above described derivatized polycarboxylate water reducing dispersant, in combination with an accelerator for concrete. In one embodiment, the compatabilizing admixture comprises a derivatized polycarboxylate dispersant comprising a polymer of the general structure shown below: 
where:
D=a component selected from the group consisting of the structure d1, the structure d2, and mixtures thereof;
X=H, CH3, C2 to C6 Alkyl, Phenyl, Substituted Phenyl such as p-Methyl Phenyl, Sulfonated Phenyl;
Y=H, xe2x80x94COOM;
R=H, CH3;
Z=H, xe2x80x94SO3M, xe2x80x94PO3M, xe2x80x94COOM, xe2x80x94OR3, xe2x80x94COOR3, xe2x80x94CH2OR3, xe2x80x94CONHR3, xe2x80x94CONHC(CH3)2 CH2SO3M, xe2x80x94COO(CHR4)nOH where n=about 2 to about 6;
R1, R2, R3, R5 are each independently xe2x80x94(CH2CHRO)mR4 random copolymer of oxyethylene units and oxypropylene units where m=about 10 to about 500 and wherein the amount of oxyethylene in the random copolymer is from about 60% to 100% and the amount of oxypropylene in the random copolymer is from 0% to about 40%;
R4=H, Methyl, C2 to about C6 Alkyl, about C6 to about C10 aryl;
M=H, Alkali Metal, Alkaline Earth Metal, Ammonia, Amine, Substituted Amine such as triethanol amine, Methyl, C2 to about C6 Alkyl;
a=0 to about 0.8, preferably 0 to about 0.6, and most preferably 0 to about 0.5;
b=About 0.2 to about 0.99, preferably about 0.3 to about 0.99, and most preferably about 0.4 to about 0.99;
c=0 to about 0.5, preferably 0 to about 0.3, and most preferably 0 to about 0.1;
d=0 to about 0.5, preferably 0 to about 0.3, and most preferably 0 to about 0.1;
xe2x80x83and
xe2x80x83wherein a, b, c, and d represent the mole fraction of each unit and the sum of a, b, c, and d is 1.0, and wherein at least one of c and d is greater than 0.